1. Field of the Invention
This invention relates generally to the field of valve actuation mechanisms and more particularly to a fail safe valve actuating apparatus.
2. Description of the Art
In the field of valve actuators, it is known to provide a fail safe mechanism for actuating a valve, typically from the open to the closed position, when electrical power is intentionally or accidentally interrupted to the valve actuator. Such valve actuators typically utilize some type of a solenoid to operate the valve between the open and closed positions. An example of an application for the use of a fail safe valve actuator is in the agricultural field such as in the application of anhydrous ammonia (NH.sub.3) or other materials. For example, in the agricultural application of anhydrous ammonia, typically a tractor is pulling an implement for applying the anhydrous ammonia from a storage tank contained on the implement or on a trailer towed by the implement. Typically, the valve actuator is used to open and close the valve remotely from the cab of the tractor. Accordingly, it is desired to have a fail safe actuator mechanism such that upon accidental or intentional interruption of power to the actuator, the actuator will shut off the valve to prevent the escape of anhydrous ammonia. For example, if the tractor was unintentionally separated from the implement carrying the anhydrous ammonia, it is desired to have the actuator mechanism shut off the valve to prevent escape of anhydrous ammonia.
Various valve actuator mechanisms are known in the art. For example, U.S. Pat. No. 4,289,038 and U.S. Pat. No. 4,113,063 both disclose actuator mechanisms which provide a fail safe mechanism under emergency or other conditions. Such mechanisms involve a complex mechanism with numerous moving parts and are not designed for use in a harsh environment such as described above.
What is needed is a fail safe valve actuator which is capable of controlling a valve from a remote location while also providing a fail safe mechanism for shutting off the valve when power is interrupted, either accidentally or intentionally, to the actuation mechanism. Further, a valve actuation mechanism is needed which provides for simple, dependable operation while operating in a harsh environment such as in conjunction with the application of materials in an agricultural setting.